Marine radar transmission and reception system

ABSTRACT

A marine radar transmission and reception system in which first and second transmission pulse radar waves are emitted as first and second pulse radar waves from first and second radar antennae or a common radar antenna; reflected waves of the first and second emitted pulse radar waves are received as first and second received pulse radar waves by the first and second radar antennae or the common radar antenna; the modes of the first and second transmission pulse radar waves are selected in cooperation with those of the first and second radar antennae or that of the common radar antenna so that the first and second received pulse radar waves may be received by the first and second radar antennae or the common radar antenna independently of each other; a quotient or difference output corresponding to the quotient or difference of the first and second received pulse radar waves or the first and second received outputs based thereon is obtained; and sea clutter eliminated received pulse radar waves or outputs based thereon that signal components of the period-in which the quotient or difference output exceeds one predetermined threshold value or lies between two threshold values-are eliminated or suppressed, are obtained.

United States Patent [:91

Nirasawa et a1.

[451 July 1, 1975 1 MARINE RADAR TRANSMISSION AND RECEPTION SYSTEM [75]Inventors: Tomiji Nirasawa, Kanagawa-ken;

I-Iiroshi Ota, Tokyo, both of Japan [73] Assignee: Kabushiki KaishaTokyo Keiki, 1 1

Tokyo, Japan [22] Filed: May 8, I973 [21] Appl. No.: 358,456

[30] Foreign Application Priority Data May 10, 1972 Japan 4746033 [52]U.S. Cl. 343/171 R; 343/7 A [51] Int. Cl G015 9/06;G01s 7/28 [58] Fieldof Search 343/17.1 R, 17.2 R, 16 R, 343/7 A [56] References Cited UNITEDSTATES PATENTS 2,901,747 8/1959 Sunstein 343/171 R 2,994,0 8O 7/1961Varela 343/17.[ R 3,126,543 3/1964 Reed 343/17.] R 3,149,333 9/1964Campbe11.... 343/17.1 R 3,189,900 6/1965 Raabe r 343/16 R 3,273,1479/1966 Herscouki... 343/171 PF 3,374,478 3/1968 Blau 343/171 R 3.6465552/l972 Atlas... 343/171 R 3,668,702 6/1972 Jones 343/171 R 3,761,9229/1973 Evans 343/171 R rccv-ccnf [tom-0cm 5C0 iiniimi .1 [(ECl-ECZ)(BCI-BCZJ sc o (ECl-ECZ) (FC1FC2)=GC (Acetic?) A0 A02 mm mums 221 222AC1 AC2 'JI/ i 7 FCZ. ACO

\couwo. mm w cw r, at

Primary ExaminerMaynard R. Wilbur Assistant Examiner- 0. E. MontoneAttorney, Agent, or FirmMarshal1 & Yeasting ABSTRACT A marine radartransmission and reception system in which first and second transmissionpulse radar waves are emitted as first and second pulse radar waves fromfirst and second radar antennae or a common radar antenna; reflectedwaves of the first and second emitted pulse radar waves are received asfirst and second received pulse radar waves by the first and secondradar antennae or the common radar antenna; the modes of the first andsecond transmission pulse radar waves are selected in cooperation withthose of the first and second radar antennae or that of the common radarantenna so that the first and second received pulse radar waves may bereceived by the first and second radar antennae or the common radarantenna independently of each other; a quotient or difference outputcorresponding to the quotient or difference of the first and secondreceived pulse radar waves or the first and second received outputsbased thereon is obtained; and sea clutter eliminated received pulseradar waves or outputs, ased thereon that signal components of the perio'in which the quotient or difference output exceeds one predeterminedthreshold value or lies between two threshold values-are eliminated orsuppressed, are obtained.

4 Claims, 16 Drawing Figures DE ECYOR t 1" NEW mm 1111 PATENTEnJuL 1SHEET NQE h I MARINE RADAR TRANSMISSION AND RECEPTION SYSTEM BACKGROUNDOF THE INVENTION l. Field of the Invention This invention relates to amarine radar transmission and reception system.

2. Description of the Prior Art In marine radar transmission andreception, there are some occasions where sea clutter based on reflectedwaves from the surface of the sea gets mixed in received pulse radarwaves based on reflected waves from a target. (The sea clutter is mixedin the received pulse radar waves while being superimposed thereonconcurrently or not concurrently and, of course, it is not always mixedin the latter.) Accordingly, in a marine radar transmission andreception system, it is necessary to obtain received pulse radar wavesor a received output based thereon from which the influence of the seaclutter has been eliminated.

To this end, various attempts have heretofore been made. It is thepractice in the prior art that where the level of sea clutter is higherthan a predetermined one, the clutter of the higher level is removedfrom received pulse radar waves or a received output based thereon, orthat where the level of the sea clutter is equal to or a little higherthan that of the received pulse radar waves, the clutter is eliminatedfrom the received pulse radar waves or the received output basedthereon, together with its one portion. Consequently, the conventionalmarine radar transmission and reception system has a defect such thateven if the level of the received pulse radar waves is relatively high,the received pulse radar waves or the received output based thereon isunnecessarily lost or that if such an unnecessary loss of the receivedpulse radar waves or received output is prevented, the influence of thesea clutter cannot be neglected.

SUMMARY OF THE INVENTION Accordingly, this invention is to provide amarine radar transmission and reception system which avoids theabovesaid defect encountered in the prior art and which effectivelyexcludes or suppresses the influence of the sea clutter mixed in thereceived pulse radar waves from or in the received pulse radar waves orthe received output based thereon.

Other objects, features and advantages of this invention will becomeapparent from the following description taken in conjunction with theaccompanying drawmgs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing oneexample of this invention.

FIG. 2 is a graph showing a (S /S g)\.S.a curve, for explaining theexample of FIG. 1',

FIGS. 3 to 5, inclusive, are block diagrams illustrating other examplesof this invention;

FIG. 6 is a graph, similar to FIG. 2, showing an X(= S )/S 2Il',S.acurve;

FIGS. 7 to 10, inclusive, are block diagrams illustrating other examplesof this invention;

FIG. 11 is a circuit diagram ofa circuit equivalent to divider circuitsemployed in the examples of FIGS. 1, 3 to 5 and 7 to 10; and

FIGS. 12 to 16, inclusive, are block diagrams illus trating otherexamples of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In general, a received electricpower S of received pulse radar waves based on reflected waves from atar get in the radar transmission and reception system is expressed inthe following form:

PAU

where P is the peak value of transmitting power of the pulse radarwaves, A the radiation area of a radar an tenna, 0' the radar crosssection or effective reflection sectional area of the target, A thecarrier wavelength of the pulse radar waves and R the distance to thetarget.

Thus, the received power S of the received pulse radar waves in theradar transmission and reception system is usually given by the equation(1) but, in the marine radar transmission and reception system, seaclutter based on reflected waves from the surface of the sea gets mixedin received pulse radar waves based on reflected waves from a targetsuch as a ship or the like, as described previously. The received powerof the received pulse radar waves based on the reflected waves from thetarget and the received power of the sea clutter based on the reflectedwaves from the surface of the sea are identified as S and S respectivelyin this specification. Since mainly the radar cross section 0 among theparameters on the right side of the equation l varies dependent uponwhether the received waves are those reflected from the target or thesurface of the sea, the radar cross section (I in the cases of thereceived waves being those reflected from the target and the surface ofthe sea are identified as 0,, and a, respectively in this specification.Accordingly, 5,, and S are expressed by the following equations:

By the way, our experiments have revealed the following facts inconnection with the radar cross sections a and 0;. given by theequations (2a) and (2b) respectively.

A. Each of 01, and 0' depends on the mode of polarization of pulse radarwaves transmitted from the radar antenna supplied with transmissionpulse radar waves, that is, whether the transmitted pulse radar wavesare of vertical polarization or horizontal polarization.

B. Each of 0 and 0' depends on the carrier wave length A of thetransmission pulse radar waves in a mode expressed by a function 0-: FM)to )t, F()\) being not expressed by F()\) :1: )3.

C. Each of 0' and 0,. depends on the pulse width 1- of the transmissionpulse radar waves in a mode expressed by a function a x F(r) to 1.

D. Each of 0', and 0, depends on the beam width 6 of the transmissionpulse radar waves, emitted in the form of a beam from the radar antenna,in a mode expressed by a relation 0' a: F(0) to 9.

a-l. Where the pulse radar waves emitted from the radar antenna are ofvertical polarization, and

a-2. Where the pulse radar waves from the radar antenna are ofhorizontal polarization, if the radar cross sections in the case of thetarget are taken as 0 and m respectively and if the radar cross sections0,. in the case of the surface of the sea are taken as a and arespectively, the following relation is obtained:

um m:

c-l. Where the pulse width 1' of the transmitted pulse radar waves isrelatively large (the pulse width 1' in this case being taken as T andC-2. Where the pulse width 1' of the transmitted pulse radar waves isrelatively small (the pulse width 1' in this case being taken as 7 ifthe radar cross sections on, in the case of the target are taken as (rand (r respectively and if the radar cross sections cr in the case ofthe surface of the sea are taken as 0' and a respectively, the followingrelation is obtained:

un m d- I. Where the beam width 6 of the transmitted pulse radar wavesis relatively large (the beam width 6 in this case being taken as 9,),and

d-2. where the beam width 6 of the transmitted pulse radar waves isrelatively small (the beam width 6 in this case being taken as 9 if theradar cross sections 0' in the case of the target are taken as 0 and mrespectively and if the radar cross sections 0' in the case of thesurface of the sea are taken as U and 0 respectively, the followingrelation is obtained:

un m 1 mm rrrz or suppressed from or in received pulse radar waves froma target or the resulting received output.

FIG. I is a block diagram showing one example of this invention which isbased on the aforesaid relation given by the equation (3a). In FIG. 1,reference numeral 1A0 indicates a transmitter circuit, which is suppliedwith a trigger pulse AAO from a trigger pulse generator circuit 2, andfrom which are derived transmission pulse radar waves 8A0 of such a modethat a carrier having a sufficiently short wavelength A is on" in theperiod of the pulse width 1' of the trigger pulse AAO. The pulse radarwaves 8A0 thus obtained are distributed by a distributor circuit 3 aspulse radar waves BA] and BAZ of substantially equal power. and they aresupplied to radar antennae 5A] and 5A2 through transmitting sideterminals of transmission and reception switching circuits 401 and 402respectively. In this case, the antennae SA] and 5A2 are identical inconstruction with each other except that they are adapted to emittherefrom the pulse radar waves BA] and 8A2 as pulse radar waves CA] andCA2 of vertical and hori zontal polarization modes respectively.

Consequently, the pulse radar waves CA] and CA2, which are ofsubstantially the same power but of vertical and horizontal polarizationmodes respectively, are respectively emitted in the form of beams of thesame width 6 from the antennae 5A1 and 5A2 in the same direction. Thetwo beams of the emitted pulse radar waves CA] and CA2 simultaneouslyirradiate substantially the same area defined by their beam width 6thereby to obtain composite reflected waves DAO and those components ofthe composite reflected waves DAO which are based on the pulse radarwaves CA] and CA2 are received individually. These received outputs areobtained as received pulse radar waves EAl and EAZ through the receivingterminal sides of the transmission and reception switching circuits 401and 402 respectively.

The received pulse radar waves EAl and EA2 thus obtained are supplied toreceiving circuits 6A1 and 6A2 each including a frequency converter, anintermediate-frequency amplifier circuit, a detector circuit, a detectedoutput amplifying circuit and so on respectively, from which are derivedequal received pulse waves FAI and FA2 based on the received pulse radarwaves EA] and EAZ. These received pulse waves FA] and FAZ are applied toan adder circuit 7 to derive therefrom an added output GA of thereceived pulse waves FAl and FAZ and the added output GA is supplied asreceived pulse waves HA through a gate circuit 8 to a system followingthe detected output amplifying system of usual radar apparatus.

In this case, the gate circuit 8 is controlled in the fol lowing manner.Namely, the received pulse waves FAl and FA2 derived from the receivingcircuits 6A1 and 6A2 are supplied to a divider circuit 9, from which isderived an output IA corresponding to the quotient of the received pulsewaves FAl and FA2 and the output [A is applied to a threshold valuedetector circuit 10. While the threshold detector circuit 10 is suppliedwith a threshold value set output JA fram a threshold value settingcircuit 11A. Where the level of the quotient out put IA is higher (orlower) than that of the threshold value set output JA, a threshold valuedetected output KA is derived from the threshold value detector circuit10 and the gate circuit 8 is turned off by the threshold detected outputKA.

The above is one example of this invention based on the relation of theequation (311). With such an arrangement, if received powers of thereceived pulse radar waves EAI and EA2 are taken as S and 5,,respectively and if these received powers 5 and S in the case of thereflected waves DAO being those from a target are taken as S and Srespectively, it will be apparent that since the radar cross sections 0'in this case are o and m as described previously, the following relationcan be obtained based on the equation (21:):

rrr) Further, if the received powers S, and 8,, in the case of thereflected waves DAO being those from both the target and the surface ofthe sea at the same time are taken as S and S respectively, it will alsobe understood that the following relation can be obtained:

lllll ST!" a $0112 f"! "r" The equation (60) expresses the relationbetween S and S in the case where the phase difference Q5, between thephase da of the carrier of the received pulse radar waves BA! in thecase of the reflected waves DAO being those from a target and that (1)of the carrier in the case of the reflected waves being those from thesurface of the sea is zero, that is, (rb da r12, 0, and the phasedifference (b g between the phases 6 and da of the carriers of thereceived pulse radar waves EAZ corresponding to da and 4),, respectivelyis zero, that is, (da da (b g O, and hence da $02 bl:

Accordingly, if output values having the same proportional constant,corresponding to a a a and a predetermined value or, within the range of01 to a are taken as E,,,,, E and E,,,,, if the value of the thresholdvalue detected output JA derived from the threshold value settingcircuit 11A is selected at E corresponding to or, and if the reflectedwaves DAO are those from the target only, the quotient output lA derivedfrom the divider circuit 9 has the value E corresponding to 01Consequently, the output E has a value outside of the range of E to E(which value, however includes E so that the threshold value detectedoutput KA is not derived from the threshold value detector circuit 10and the added output GA passes through the gate circuit 8. On the otherhand, assuming that the reflected waves DAO are only those from thesurface of the sea, the quotient output IA has the value E correspondingto a a so that the output E is obtained having a value outside of therange from E to E and the threshold value detected output KA is providedas representing that the value of the output IA is larger (or smaller)than that of the output .lA. Consequently, the added output GA isprevented from passing through the gate circuit 8. Assuming that thereflected waves DAO are those from both the target and the surface ofthe sea, the quotient output IA has the value E corresponding to a a ofthe equation (6a) and this value E is within the range from E,,,, to EAccordingly, where the value E lies within the range from E,,,, to E thethreshold value detected output KA is obtained to inhibit the passage ofthe added output GA through the gate circuit 8. While, where the value Eis within the range from E to E the threshold value detected output KAis not produced and the added output GA passes through the gate circuit8.

Therefore, where sea clutter based on the reflected waves from thesurface of the sea is mixed in the received pulse waves GA in such amanner that the quotient output lA from the divider circuit 9 exceedsthe value E within the range from that E corresponding to a of theequation (40) to thaflE corresponding to a of the equation (5a) towardsthe value E,.,,, the re ceived pulse waves HA derived from the gatecircuit 8 is obtained in the form of such an output that a signal of theperiod, in which the above sea clutter is mixed in the received pulsewaves GA, is removed therefrom. This relation will be described moreconcretely. If 0: expressed by the equation (4a) is considered in 21normalized form 01 l, or expressed by the equation (5a) has a relationthat a I. If, now, a 5 statistically, the abovesaid a, is selected, forexample, at about 4.64 within a range from 1 to 5 Considering the valueE of the quotient output IA corresponding to 01 in a normalized form asE l, the value E of the quotient output IA corresponding to a isrepresented as 5 and the value of the threshold value set output JAcorresponding to a is expressed as E, 464. Accordingly, where thereflected waves DAl) are those from the target only, the quotient output[A is that E l and since E E,,,, the threshold value detected output KAis not produced and the added output GA passes through the gate circuit8. Where the reflected waves are those from the surface of the sea only,the quotient output IA is that E 5 and since E E,,,,, the output KA isprovided and the output GA is prevented from passing through the gatecircuit 8. Where the reflected waves DAO are those from both of thetarget and the surface of the sea, the quotient output IA is E lying inthe range of E l to E 5, so that if the value of E lies within the rangeof E l to E 4.64, the output KA is not obtained and the added output GApasses through the gate circuit 8. If the value of E lies within therange of E,,,, 4.64 to E 5, the output KA is produced and the addedoutput GA does not pass through the gate circuit 8. Accordingly, wheresea clutter resulting from the reflected waves from the surface of thesea is mixed in the received pulse waves GA in such a relation that thequotient output IA exceeds E, 4.64 the received pulse waves HA derivedfrom the gate circuit 8 are obtained having removed therefrom a signalof the period in which the sea clutter is mixed.

This will become more apparent from the curve of FIG. 2 drawn on theassumption that d dz 0, a E l, a E 5 and a, E, 4.64, the abscissarepresenting S /8 and the ordinate a E Rewritten by using a and a theequation (6a) becomes as follows:

tir: m:

and substituting a 5 and 01 l in the above equa tion (60'), thefollowing equation is obtained:

Based on this, S in the equation (6a") is used in the abscissa.

Accordingly, the foregoing example of this invention has an advantagethat received pulse radar waves having effectively removed therefrom seaclutter can be obtained without incurring such a defect of theconventional marine radar transmission and reception system as describedpreviously.

Referring now to FIG. 3, a description will be given of another exampleof this invention which is based on the relation given by the aforesaidequation (3b). In FIG. 3, reference numerals 1B] and ]B2 designatetransmitter circuits respectively, which are supplied with a triggerpulse ABC of the pulse width 1 from the trigger pulse generator circuit2 and from which are derived transmission pulse radar waves BBl and BB2of such modes that carriers having wavelengths A, and A (A, M) are "on"in the period of the pulse width 1' of the trigger pulse ABO. Thesepulse radar waves BB] and BB2 are supplied to radar antennae 5B] and 582through transmitting side terminals of the transmission and receptionswitching circuits 40] and 402 respectively. In this case, the antennae5B] and 582 are identical in construction with each other except thatthey are designed for the carriers A, and A respectively.

Consequently. pulse radar waves CB1 and CH2 based on the transmissionpulse radar waves BB] and BB2, which are of substantially the same powerbut include the carriers of the wavelengths A, and A respectively, arerespectively emitted in the form of beams of the same width 6 from theantennae 5B] and 582 in the same direction. The two beams of the emittedpulse radar waves CB] and CB2 provide composite reflected waves DB0 andthose components of the composite reflected waves DBO which are based onthe emitted pulse radar waves respectively are individually received.These received outputs are obtained as received pulse radar waves EB]and EB2 through receiving terminal sides of the transmission andreception switching circuits 401 and 402 respectively.

The received pulse radar waves EB] and EB2 thus obtained arerespectively supplied to the receiving circuits 6B1 and 6B2 eachincluding a frequency converter, an intermediate-frequency amplifyingcircuit, a detector circuit and a detected output amplifying circuit,from which are derived the same detected received waves FBI and FB2based on the received pulse radar waves EB] and EB2 respectively. Thereceived radar waves FBI and FB2 are applied to an adder circuit 7 and adivider circuit 9 as is the case with FIG. Received pulse waves GBderived from the adder circuit 7 are fed to the gate circuit 8 to derivetherefrom received pulse waves HB. While, a quotient output 18 derivedfrom the divider circuit 9 are supplied to the threshold value detectorcircuit 10 which is supplied with a threshold value set output .lB froma threshold vaiue setting circuit llB. Where the value of the quotientoutput IB is larger (or smaller) than that of the threshold value setoutput .113, a threshold value detected output KB is derived from thethreshold value 0 detector circuit 10, by which the gate circuit 8 iscontrolled to be turned off.

The above is one example of this invention based on the relation of theaforementioned equation (3h). With such an arrangement as is the casewith the example of FIG. 1, if received powers of the received pulseradar waves EB] and EB2 are taken as S,,, and S respectively, if thereflected waves DBO are those from a target and if the received powers Sand S in the case of the reflected waves DBO being those from thesurface of the sea are taken as S and S S and S respectively, it will beapparent that since the radar cross sections 0' in these cases are 0 andm 0- and a respectively as described previously, the following relationsare obtained based on the equations l and (2) where A is a constant. Itwill also be apparent that if the received powers S and S in the case ofthe reflected waves being those from both the target and the surface ofthe sea are taken as S and S respectively, the following relation isobtained:

till] un orm The equation (6b) expresses the relation between Ocb] S andS in the case where the phase difference (1),, between the phase (1),,of the carrier of the received pulse radar waves EB] in the case of thereflected waves DBO being those from the target only and that 42 of thecarrier in the case of the reflected waves being those from the surfaceof the sea is zero, that is, dz dz d) O, and the phase difference dabetween the phases da and Q5, corresponding to (s and (p respectively iszero, that is, ((1) da bin 0, and hence 01 1: d

Accordingly, if output values having the same proportional constant,corresponding to a 0r a and a predetermined value a, within the rangefrom a to a are taken as E E E and E respectively and if the value ofthe threshold value set output 1B is selected at E corresponding to athe quotient outputs [8, which are derived from the divider circuit 9 inthe cases where the reflected waves DBO are only those from the target,only those from the surface of the sea and those from both of them, havethe values E E and E corresponding to a a and a respectively, as is thecase the example of FIG. Therefore, where sea clutter resulting from thereflected waves from the surface of the sea is mixed in the receivedpulse waves GB in such a manner that the quotient out-

1. A marine radar transmission and reception system comprising: a. meansfor sequentially generating first and second transmission pulse radarwaves of first and second pulse widths, respectively; b. an antenna forsequentially emitting the first and second transmission pulse radarwaves in the same direction as first and second emitted pulse radarwaves respectively and sequentially receiving first and second reflectedpulse radar waves of the first and second emitted pulse radar waves; c.a receiving circuit supplied with the output of the antenna; d. meansfor producing first and second received pulse waves corresponding to thefirst and second reflected pulse radar waves from the output of thereceiving circuit, respectively; e. a gate circuit for gating the outputof the receiving circuit or either one of the first and second receivedpulse waves; and f. control means having a quotient circuit forproducing the quotient output of the first and second received pulsewaves, a setting circuit for deriving a predetermined threshold valueoutput and a detector for detecting whether or not the quotient is inexcess of the threshold value output; g. in which the gate circuit iscontrolled with the output of the detector of the control means, wherebysea clutter eliminated received pulse radar waves are obtained from thegate circuit.
 2. A marine radar transmission and reception systemcomprising: a. means for generating transmission pulse radar waves; b.first and second antennae for sequentially emitting the transmissionpulse radar waves in the same direction as first and second emittedpulse radar waves of first and second beam widths respectively andsequentially receiving first and second reflected pulse radar waves ofthe first and second emitted pulse radar waves respectively; c. areceiving circuit supplied with the outputs of the first and secondantennae; d. means for producing first and second received pulse wavescorresponding to the first and second reflected pulse radar waves fromthe output of the receiving circuit, respectively; e. a gate circuit forgating the output of the receiving circuit or either one of the firstand second received pulse waves; and f. control means having a quotientcircuit for producing the quotient output of the first and secondreceived pulse waves, a setting circuit for deriving a predeterminedthreshold value output and a detector for detecting whether or not thequotient is in excess of the threshold value output; g. in which thegate circuit is controlled with the output of the detector of thecontrol means, whereby sea clutter eliminated received pulse radar wavesare obtained from the gate circuit.
 3. A marine radar transmission andreception system comprising: a. means for sequentially generating firstand second transmission pulse radar waves of first and second pulsewidths, respectively; b. an antenna for sequentially emitting the firstand second transmission pulse radar waves in the same direction as firstand second emitted pulse radar waves respectively and sequentiallyreceiving first and second reflected pulse radar waves of the first andsecond emitted pulse radar waves; c. a receiving circuit supplied withthe output of the antenna; d. means for producing first and secondreceived pulse waves corresponding to the first and second reflectedpulse radar waves from the output of the receiving circuit,respectively; e. a parallel circuit of first and second gate circuitsgating the output of the receiving circuit or either one of the firstand second received pulse waves; and f. control means having a quotientcircuit for producing the quotient of the first and second receivedpulse waves, first and second setting circuits for deriving first andsecond predetermined threshold value outputs respectively, and first andsecond detectors for detecting whether or not the quotient is in excessof the first and second threshold value outputs respectively; g. inwhich the first and second gate circuits are controlled with outputs ofthe first and second detectors of the control means, respectively,whereby sea clutter eliminated received pulse waves are obtained fromthe parallel circuit.
 4. A marine radar transmission and receptionsystem comprising: a. means for generating transmission pulse radarwaves; b. first and second antennae for sequentially emitting thetransmission pulse radar waves in tHe same direction as first and secondemitted pulse radar waves of first and second beam widths respectivelyand sequentially receiving first and second reflected pulse radar wavesof the first and second emitted pulse radar waves respectively; c. areceiving circuit supplied with the outputs of the first and secondantennae; d. means for producing first and second received pulsecorresponding to the first and second reflected pulse radar waves fromthe output of the receiving circuit, respectively; e. a parallel circuitof first and second gate circuits gating the output of the receivingcircuit or either one of the first and second received pulse waves; andf. control means having a quotient circuit for producing the quotient ofthe first and second received pulse waves, first and second settingcircuits for deriving first and second predetermined threshold valueoutputs respectively, and first and second detectors for detectingwhether or not the quotient is in excess of the first and secondthreshold value outputs respectively; g. in which the first and secondgate circuits are controlled with outputs of the first and seconddetectors of the control means, respectively, whereby sea cluttereliminated received pulse waves are obtained from the parallel circuit.